textproduct: Quad Cities

KEY MESSAGES

- Oppressively hot and humid through this evening, with heat indices in many locations peaking around 105-115 degrees.

- Organized thunderstorms are possible this afternoon into this evening in northwest Illinois, though there remains some uncertainty due to capping and the track. Some of these storms may be strong to severe with damaging winds if well- organized. An Enhanced (level 3 of 5) risk of severe thunderstorms is in effect for northwest Illinois.

- Some midweek relief comes behind a cold front tonight, although smoke from Northwest U.S. and Canadian fires may spread over the area that could continue through Tuesday.

SHORT TERM /THROUGH TONIGHT/

Issued at 301 AM CDT Mon Jul 27 2026

A complicated forecast is in store for Monday, but amidst the many different ways today could play out, there is one consistent factor: it will be oppressively hot and humid. Early morning temperatures remain quite warm in the upper 70s to low 80s, with dew points not far behind. Combined with weak surface winds, this warm and humid airmass has allowed for the development of patchy areas of fog and low stratus north of Interstate 80. This also includes areas of dense fog east of the Quad Cities metro. Diurnal heating and quickly increasing temperatures will allow any fog to burn off by mid-morning.

Once the fog clears out, the surface will quickly heat up, leading to yet another oppressively hot and humid day. Highs are forecast in the low to mid 90s, with some areas in the far south reaching into the upper 90s. Dew points are once again expected to reach into the lower 80s today, leading to heat indices as high as 105 to 115 degrees. An Extreme Heat Warning is in effect area- wide. However, there is a potential limiter in how hot we can get today: thunderstorms.

Guidance remains keen on a potential MCS moving through parts of northern Illinois today, though there is quite the range of solutions, including a some that have no storms at all. This is likely due to the strong environment that will be in place: 30-40 kts of shear, high instability from a hot and humid airmass, and ample moisture with PWATS near 2 inches. Given this potent environment, SPC has an Enhanced (level 3 of 5) in place for northwest Illinois and a Slight (level 2 of 5) to the Interstate 380/Highway 218 corridor. However, forecast confidence is quite low, with the most likely scenario being low storm coverage. This is due to a number of factors, with perhaps the greatest of these being warm temperatures aloft. While capping will be weak with 850mb temperatures around 20-25 degC, it could suppress any convection, such as was seen yesterday. If storms do develop, there are still a few scenarios that could play out.

Scenario 1: Storms develop across Wisconsin and move south- southeastward as an MCS. This MCS matures prior to reaching Illinois early to mid afternoon, allowing for it to produce swaths of damaging winds and torrential rainfall as it moves through northern Illinois. In this scenario, the MCS tracks to the east of our CWA. While the fringes of the MCS could still impact parts of our CWA across northwest Illinois, damaging winds would have a lower probability but still be an area of concern.

Scenario 2: Similar to Scenario 1, storms develop across Wisconsin, with the main difference being a more westward track. This would result in the MCS tracking over our CWA's northwest Illinois counties, and slight shifts could result in parts of eastern Iowa along the Mississippi River seeing a few storms. In this scenario, the potential for damaging winds, including significant winds, is higher. The primary impacts would be focused in northwest and north-central Illinois.

By evening, the cold front will begin making its way through the CWA, slowly pushing southward. While this may not offer immediate relief in temperatures, it will help reduce heat indices and the chances for heat headlines in the coming days.

LONG TERM /TUESDAY THROUGH SUNDAY/

Issued at 301 AM CDT Mon Jul 27 2026

Once the front passes through, Tuesday will feel much cooler as more seasonable temperatures return. One note for behind the front is the potential for smoke in the air, possibly even reduced air quality at the surface. GOES Geocolor satellite Sunday afternoon indicated widespread smoke over the northern CONUS Rockies into the western Dakotas. RAP and HRRR extended smoke forecasts indicate this being steered southward behind the front over our area. This is still too far out to tell if it would mix to near- surface, but at least some smoky sky tonight into early Tuesday looks probable.

After quiet and near to slightly warmer than seasonable temperatures Wednesday and into the day Thursday, a slow moving and fairly well-defined short wave is indicated by guidance to pass over the area late Thursday night into Friday. This looks like the next chance of rain.

AVIATION /06Z TAFS THROUGH 06Z TUESDAY/

Issued at 1249 AM CDT Mon Jul 27 2026

Current satellite imagery shows the development of a low stratus deck from the Mississippi River eastward into northwest Illinois, along with mid to high clouds moving southward. Clear skies and high humidity tonight will support the development of areas of shallow patchy fog, as seen already at DBQ. This could lead to temporary MVFR to IFR VSBYs through daybreak.

Of note is great uncertainty in convective potential through the TAF period. Guidance has been quite mixed in how storms are to develop and evolve this morning, including time of arrival being pushed back with each run. As such, the PROB30s for DBQ/MLI have been removed from this issuance due to high uncertainty in when and where storms may occur. Towards afternoon(27/18-23Z), there is increasing confidence in isolated to scattered showers and storms in southern Iowa. Uncertainty in eastward extent has kept any PROB30 mention from BRL at this time.

Winds will be light and variable overnight before strengthening and becoming gusty and southwesterly through the day. Towards the end of the period, winds will turn northwesterly with the passage of a front.

DVN WATCHES/WARNINGS/ADVISORIES

IA...Extreme Heat Warning until 10 PM CDT this evening for IAZ040>042-051>054-063>068-076>078-087>089-098-099. IL...Extreme Heat Warning until 10 PM CDT this evening for ILZ001- 002-007-009-015>018-024>026-034-035. MO...Extreme Heat Warning until 10 PM CDT this evening for MOZ009- 010.